Color Wise Mask
Masks in image editing software are a way of protecting specific areas of image, just as we would use masking tape when painting our house. A mask consists of a gray scale channel, called an alpha channel and is often displayed as a ruby overlay so the underlying image can be seen through the mask. The darkest areas of a mask are the areas most protected and the white areas are unprotected. Shades of gray represent areas of partial protection that corresponds with the level of gray.
A mask is like a stencil placed over the image that allows us to edit only a part of the image while the rest area covered by the stencil - is protected. Both the protected area and the selection can be edited. In addition, we can use masks for other complex editing tasks - for example, to apply color changes or filter effects to an image.